1. Field of the Invention
The present invention relates to a data conversion apparatus and method which convert m-bit data into n-bit data.
2. Description of the Related Art
Generally, binary data recorded on an optical disk is converted (modulated) into a code with a suppressed DC component. The minimum number of “0” bits between “1” bits in the converted (modulated) code sequence is represented by d. The maximum number of “0” bits between “1” bits is represented by k. The code used for modulation is called a (d, k) code.
A current DVD (Digital Versatile Disk) employs a (2, 10) code for modulation. In recent years, the data playback technology from optical disks has improved, and a PRML (Partial Response Maximum Likelihood) technique is employed. Accordingly, employment of a “d=1” modulation code suitable for a high density has been examined.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2000-105981 (reference 1) discloses a technique in which the above-described “d=1” modulation code is employed, and additionally, a DC suppressing inversion bit is added to the end of a converted code.
In addition, Jpn. Pat. Appln. KOKAI Publication No. 2000-332613 (reference 2) discloses a technique in which the above-described “d=1” modulation code is employed to convert 4-bit data into 6-bit data.
In the technique disclosed in reference 1, however, since 8-bit data is converted into 12-channel bit data, 28=256 or more conversion patterns are necessary. As a result, the conversion table size becomes large, and modulation/demodulation processing (conversion processing) is complicated.
In the technique disclosed in reference 2, since 4-bit data is converted into 6-channel bit data, only 24=16 conversion patterns suffice. As a consequence, the conversion table size is small. However, since the conversion table requires four states, the problem of complex modulation/demodulation processing is not solved.